All required grounds are in place to the recommended places (bare metal contact etc).
Wiring has all been meticulously gone over, everything is in the right place according to the diagrams found here and on Ktuned's site.

I originally had no issues with the ecu when I first finished the build, the ecu was drop shipped from Hondata new through my friends at HPT in NC (authorized dealer). The ecu would reflash as I made changes to the maps, save the map and the fuel pump would prime during the upload phase and the car would start with no issues. Then about ~6 months ago I noticed that I the car would not start without having the Laptop USB connected to the ECU, once the laptop is plugged in and I see that it auto recognizes that it is plugged in, the car will normally start without issue. If I try to start the car without the laptop plugged in, I get a CEL and the pump wont prime. At this point, it seems like something has corrupted the map that is loaded on the Kpro as it is not sending the command to prime the pump and the car wont start.

If I wait say an hour, disconnect the battery and ecu, car cools down, plug everything back in, I can then upload the same .kal to the Kpro and it seems to be fine until the next time the car is heat cycled and shut off, then immediately attempted to be restarted.

Last night I was out getting part throttle logs, shut the car off after 45 minutes of driving, then tried to restart and same problem. Stranded for about an hour as the pump would not prime, and the Kpro would not cycle the pump when I attempted to upload the .kal that I am working with. Waited, disconnected the battery, disconnected the Kpro, waited 45 minutes or so, plugged everything back in, and whallah, upload the .kal to Kpro, fuel pump cycles during the upload and the car starts like normal (with the laptop plugged in).

Current cranking amps are 9.9-10V with 13.2~13.45V+ when running with no headlights on etc.. I see that the RSX-S requires a battery that is 400 CA my current battery has 320 CA.

What is KproV4's voltage requirement at startup? Could the low CCAs cause the map to corrupt?

I do not have access to another known running vehicle to try my ecu in. The car would start without the laptop previously without issue.

I need to get this issue resolved, it is very inconvenient during track events or when tuning to have this issue pop up (ie if I have an off and stall the car, I need to be towed off the track, I don't like that).

If the fuel pump will not prime then it is not the KPro. You can unplug and remove the KPro and the fuel pump should still prime.

A damaged ECU fuel pump output transistor is very common on the ECUs used in engine swaps. If someone before you used the ECU with incorrect wiring even once then the output driver might be bad. When it heats up a little it can't switch the fuel pump relay.

However since you said that plugging in the USB cable makes a difference, I would suspect ground current flows. In this case when you plug in the USB cable something gets grounded.

I would measure voltage difference and current flow between the ECU ground pins and the battery negative. Also from the USB shield to the battery negative. There should be little voltage difference but the main thing is that there should be very little current flow (under 10 mA).

That is interesting about the heat causing the driver not to be able to switch the signal to the pump relay. I will test that by running the car for 1-2 minutes, shutting it off and attempting to restart it. Then do the same thing but let it heat cycle the fan 4 or 5 times to make sure its warm, shut it off and try restarting. If it restarts with everything still cold but not hot, then that may be something to look into. The restart issue last night, was WITH the laptop plugged in and the car was run for a while which would agree with the heat/ecu pump relay as the issue. As far as the pump wiring and ecu signal wire, I am the only one that has used the ecu barring testing its viability before receiving shipment, the only thing I have done is run the factory chassis fuel pump 12v signal wire to a relay that I put in to operate my walboro 450 on 10g wire direct from the battery due to pump voltage drop requirements.

The other thing that I have found searching was that the smaller batteries like the D680 (being discharged fully even once, which the battery did discharge almost fully on one occasion) may not provide enough voltage at cranking causing a daughterboard error. I do have a CEL when it isn't priming the pump but I cant catch it because Kpro wont recognize that its plugged into the laptop at that point (not allowing me to investigate the CEL). I will also check the resistance to the ECU ground pins and the negative on the battery like you suggested just to rule out grounding. The car was a fresh build with no rust or anything like that so I know my ground contacts are all perfect metal to metal, resistance for all grounds are in the acceptable range.

Checked the voltage (key off) to both pins on the A connector in pin positions 4 and 5 (ecm ground) set on 20ma on my meter. 0.00 reading for both 4 and 5 pins to the negative battery terminal and 0.00 reading to the outside of the usb port to the negative battery terminal.

Checked the voltage (key off) to both pins on the A connector in pin positions 4 and 5 (ecm ground) set on 20ma on my meter. 0.00 reading for both 4 and 5 pins to the negative battery terminal and 0.00 reading to the outside of the usb port to the negative battery terminal.

Thanks

I forgot to ask, should this test be run ignition on, key off, or does it matter?

If it shows 0.00 mA then you might have blown the small fuse on the multi-meter as normally there should be some current flow.

Checked with the car on and it fluctuates between, 8.5-10.5 ma for both ecm ground pins. Usb shroud shows 0.00.

Car started with the laptop plugged in and ran for 2 minutes, shut it down, plug the lap top back in and restarted no issues. Will attempt a hot shut off and restart to see if it has issues.

Ran the car for 45 minutes or so for a good heat cycle. The ecu feels warm but not hot, the car would restart hot with the usb plugged in. I tried to start the car without the usb plugged in and it started, ran, threw a CEL and wouldnt recognize the usb when I plugged it in to check the code. Shut the car off and it wouldnt restart and started seeing the same issue with the pump not priming when I would cycle the key and the CEL was still present. Attempted to restart it with the usb plugged in and it wouldnt restart until I turned the ignition off and tried to recognize the usb a few times. Once the usb was recognized I was able to re-upload the map and it started back up. Could the non-usb start cause the ecu to corrupt the map if cranking voltage is too low (still seeing 9-10v cranking)? or for some other reason? I am at a loss with this one. Thanks again for any insight into the information I have provided.

You should not plug in the USB until you have the issue resolved or you could damage the K-Pro and the ECU.

Do those voltage values for the ecu grounds sound right?

When I start the car without the USB plugged in, the car will start the first time I try to start it, throw a CEL and NOT allow me to interface (ie will not recognize the USB) to check the CEL. After which, it will not restart with OR without the usb connected. I believe the usb interface is not active on the Kpro at this point. Then after the key is turned off, and I remove the usb from the laptop and plug it back in, it will recognize it after one or two remove and inserts into the laptop. If I at this point I dont re-upload the .kal the car will not start, if I upload the .kal, the pump cycles, and then the car restarts as normal.

Any ideas on why I would need the USB plugged in for Kpro to function properly? Everything again, is wired per the schematic on this site. Grounds are solid.

Originally it started without the need for the usb to be plugged in, NO wiring was changed or modified and it started doing this. The laptop is providing some means of power or ?? to the ecu for it to function properly.

You need to try this ECU on a known working vehicle first to make sure it has not been damaged and is working correctly. If it is then you will need to correct the wiring faults in your vehicle that are causing the issue.

You need to try this EUC on a known working vehicle first to make sure it has not been damaged and is working correctly. IF it is then you will need to correct the wiring faults in your vehicle that are causing the issue.

Do the voltage values that I posted that "Hondata" (not Doug) instructed me to check on the ECU grounds look normal?

I will see if I can find someone that will let me randomly plug my ecu into their car.... not to many options for me on that front.